1. Field of the Invention
The present invention relates to an electrophotographic toner for single- or double-component development used for developing an electric latent image or magnetic latent image by an image forming apparatus such as an electrophotographic copier and printer, and a method for manufacturing the same.
2. Description of Related Art
In recent years, new apparatuses in the field of electrophotography such as copiers and printers have been developed with the objects of reducing apparatus size, and speeding up operation time, and providing high-quality images. In terms of the size reduction, all processes of electrophotography including developing systems and fixing systems have been examined. However, regarding developers, it is desired that developer filling parts such as a toner hopper have lower capacity and a longer life. In order to realize these features, it is desirable to develop a novel toner enabling a large number of printings with a small amount of toner.
In terms of the provision of high-quality images, the following methods have been developed: a method for obtaining sharp images by controlling the particle size, the electric characteristics, or the like of a toner as a developer, or controlling the color properties of the toner such as color development, transparency, and masking (hiding) properties; and a method for obtaining high-density images by attempting to increase the content of a colorant in a toner. Also, surface printing that uses a liquid recording material (ink) is capable of providing high-density images having uniform quality with a reduced recording material thickness on a printing medium in comparison with the case of electrophotographic images. For full-color electrophotographic images, process color toners including yellow, magenta, and cyan toners are usually used in addition to black toner, and various colors are reproduced through printing by the combination of these color toners. Therefore, the recording material (toner) used for a print image causes differences in thickness depending on colors to be reproduced, and the reflection difference attributable to the thickness differences allows a user to apprehend the difference from images formed by surface printing. Hence, in order to obtain uniform, sharp, and high-quality images by electrophotography, it is necessary to form an image having less thickness and a desired image density.
The patent document (JP Patent Publication (Kokai) No. 9-114127 A (1997)) discloses that high image quality, high density, and suitability for development can be attained by optimizing toner particle diameter, pigment content, and toner deposition amount. However, merely increasing pigment concentration and optimizing particle size and deposition amount, though enabling a high optical density, do not solve problems in that full-color image formation is liable to deteriorate the chroma or decrease the reproduction range of a secondary color.
The patent document (JP Patent Publication (Kokai) No. 6-230602 A (1994)) suggests that a toner image is formed out of a magnetic toner containing at least a binder resin and a magnetic powder, and the toner image is fixed so that the height (h1) of the toner image before fixation and the height (h2) of the toner image after the fixation satisfy the condition of 2≦h1/h2≦10. The document 2 describes that a lower height of toner image after fixation can control the occurrence of stains on copied images. However, when the toner image has a low height, masking properties of the toner on a printing medium may be inferior or the toner image may be affected by irregularities of the surface of a printing medium such as paper, thus making it impossible, for example, to obtain a desired optical density.